A fuel pump is a critical component of proper engine operation. For the millions of Pontiac V-8s that left the engine assembly plant, the mechanical fuel pump was the unsung hero that received little notoriety. It quietly supplied the carburetor with an adequate amount of fuel for proper engine performance at every speed and load. It operated so reliably and consistently that, beyond complete failure, most owners simply took their Pontiac's pump for granted.
As we learned in "Ethanol Education" (HPP, Sept. '09), low-level ethanol-blend fuel is here to stay, and it appears that an increase from 10-percent (E10) to E15 is in the future. In that article we discussed how ethanol tends to cause the rubber components within a fuel system to petrify or deteriorate and fail. We found that the permanent solution for carburetors is a high-quality rebuild kit with components specifically designed for use with ethanol-blend fuel.
Through the mid-'60s, Pontiac...
Through the mid-'60s, Pontiac fuel pumps were assembled using screws or bolts. Federal-Mogul offers a retrofit, permanently-sealed Carter replacement for those applications. In the early years of Pontiac V-8 production, some fuel pumps (like this particular unit) doubled as a vacuum pump for the vacuum-operated windshield wipers. No dual-action replacements are available.
Ethanol-related failure concerns aren't just limited to carburetor components, however. Ethanol is corrosive and can attack the entire fuel system of a vintage vehicle over time. Other rubber components, like the fuel pump diaphragm and check valves, can also be affected. Fortunately for hobbyists, Federal-Mogul produces a number of stock-replacement mechanical fuel pumps for Pontiac applications in its Carter line, and all are designed for use with ethanol-blend fuel. Follow along as we explore those offerings and share suggestions from a company insider.
Mechanical Fuel Pump Basics
A fuel pump is designed to draw fuel from the tank, located at the rear of the vehicle, and deliver it to the carburetor float bowl, where it's atomized and enters the engine for consumption. A typical permanently-sealed mechanical fuel pump consists of a cast-alloy body and stamped-steel fuel cover, or canister as it's often called. An external pump arm protrudes from the pump body, and on the opposite end of the pump arm is a large internal diaphragm made of some type of rubber.
An eccentric fastened to the front of the camshaft forces the fuel-pump arm down. As the pump arm travels downward, it pivots and pulls the diaphragm upward. That creates the vacuum that draws fuel through the inlet check valve and into the fuel chamber. As the eccentric continues rotating, the fuel-pump arm pivots upward freely. The compressed diaphragm return spring pressurizes the fuel and forces it from the fuel chamber, through the outlet check valve, and toward the carburetor.
Federal-Mogul's Carter Fuel...
Federal-Mogul's Carter Fuel Delivery Products brand has been producing high-quality fuel-system components for many years. It presently offers 17 different Pontiac-specific mechanical fuel pumps that are built to OE-spec. They are completely compatible with ethanol-blend fuel. Is yours?
During normal operation, the fuel pump will not draw additional fuel into the fuel chamber once it's completely full. The fuel remains pressurized by the diaphragm return spring and the carburetor's inlet valve. As the carburetor uses fuel and its float level drops, the inlet valve opens, and fuel flows from the fuel chamber into the carburetor. Any punctures or tears to the pump's rubber diaphragm and/or rubber check valves will inhibit its ability to properly draw fuel in or push it along.
Pontiac's Pumps
Pontiac strategically placed its V-8's fuel pump on the driver side of the timing cover, where it's cooled by the engine fan. Its pumps were sourced from the AC division of General Motors. Until the mid-'60s, the AC pumps featured a cast body and fuel cover, and were fastened together using bolts or screws. Though the intended service life was around 30,000 miles, the units were serviceable and could be rebuilt using a new kit available through dealership parts departments.
On March 9, 1965, Pontiac issued Service Bulletin No. 65-84, notifying its dealership service departments that a new "disposable" fuel pump was installed on certain 421ci engines beginning in February of that year. As opposed to being fastened together with hardware, the new Unitac fuel pump-as it was marketed by AC-featured a stamped-steel canister, which was crimped around the cast-alloy body and retained the diaphragm.